feat: module 04 interceptors

Trigger multipliers as aura data on cards, snapshotted by an Aura Update
(Other) after each Death Creation Step and on summon, and applied by one
generic routine (activations) when each queued trigger starts. Baron
Rivendare is content only (stacking "max"); Brann Bronzebeard is the
content-only Expansion Drop. Adds play (now required) and Battlecry.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

course/harness.md

@@ -8,9 +8,10 @@ Each module adds functions; `start-module` prints the line for the module you st
 
 ## Part I (`Game`): additions per module
 
-- M1: `newGame(opts?: { decks?: [string[], string[]] }): Game`; `summon(card: string, player?: 0|1): Id` (to right end of board); `addToHand(card, player?)`, `addToDeck(card, player?)`; `play(handId: Id): void` (Expansion Drop); `zoneOf(id): "deck"|"hand"|"board"|"graveyard"`; `board(player): Id[]` (left to right); `hand(player): Id[]`; `orderOfPlay(id): number`; `nameOf(id): string`.
+- M1: `newGame(opts?: { decks?: [string[], string[]] }): Game`; `summon(card: string, player?: 0|1): Id` (to right end of board); `addToHand(card, player?)`, `addToDeck(card, player?)`; `play(handId: Id): void` (Expansion Drop; required from M4); `zoneOf(id): "deck"|"hand"|"board"|"graveyard"`; `board(player): Id[]` (left to right); `hand(player): Id[]`; `orderOfPlay(id): number`; `nameOf(id): string`.
 - M2: `hero(player): Id`; `dealDamage(target: Id, amount: number): void` (one Sequence); `cast(card: string, player?, target?: Id): void`; `health(id)`, `attack(id)`, `armor(player)`; `log(): GameEvent[]`; `clearLog()`.
 - M3: `destroy(target: Id): void` (marks pending-destroy, one Sequence).
+- M4: no new functions; `play(handId)` (the M1 Expansion Drop) is now required: it runs one Sequence in which the minion enters the right end of its owner's board (`Summoned{id}`), then its Battlecry resolves (`Triggered{source, trigger: "battlecry"}`). The M4 tests also use `Baron Rivendare`, `Novice Engineer` and `Twisting Nether` (the M3 Expansion Drop card).
 - M5: `registerCards(defs: CardDef[]): void`; `assemble(base: string, donor: string, half: "top"|"bottom"): string` (registers and returns new card name `"<base> (Assembled)"`; throws `AssembleError` if text unchanged).
 
 ### Side by side (Part I)
@@ -32,6 +33,7 @@ Each module adds functions; `start-module` prints the line for the module you st
 | M2 | `health(id)`, `attack(id)`, `armor(player)` | `health`, `attack`, `armor` |
 | M2 | `log()`, `clearLog()` | `log(&self) -> Vec<GameEvent>`, `clear_log(&mut self)` |
 | M3 | `destroy(target)` | `destroy(&mut self, target: Id)` |
+| M4 | `play(handId)` now required (one Sequence; Battlecry) | `play(&mut self, hand_id: Id)` |
 | M5 | `registerCards(defs)` | `register_cards(&mut self, defs: Vec<CardDef>)` |
 | M5 | `assemble(base, donor, half)` (throws `AssembleError`) | `assemble(...) -> Result<String, AssembleError>` |